1. Field of the Invention
The invention relates generally to the optical processing of line patterns or of similar data that must be processed for pattern recognition purposes and, more particularly, to automatic optical surveying of such patterns for the generation of binary coded data patterns suitable for processing or storage by digital processing or other pattern recognition apparatus.
2. Description of the Prior Art
The art is known to include optical systems for the analysis of fingerprint patterns that employ matched optical filtering or cross-correlation techniques and the direct comparison of a fingerprint image to be identified with prerecorded fingerprint images. In addition, related techniques enable comparison between the Fourier transform of a fingerprint image to be identified with prerecorded Fourier transforms of fingerprints. Such optical systems have often involved rapidly rotating, highly specialized optical filter elements generally disposed in the Fourier transform plane of an optical processor for cyclically selecting distinct components of the Fourier transform for transfer to an image plane for detection there and for subsequent processing. Data representing ridge line angular orientation is generally developed, though the spacing between ridges may also be derived. Representative concepts of this type of recognition apparatus appear in the following U.S. Pat. Nos. assigned to Sperry Rand Corporation in the name of the present inventor:
3,771,124--"Coherent Optical Processor Fingerprint Identification Apparatus", issued Nov. 6, 1973, PA1 3,771,129--"Optical Processor Fingerprint Identification System", issued Nov. 6, 1973, PA1 3,873,970--"Fingerprint Identification Apparatus", issued Mar. 25, 1975 (with W. T. Maloney), PA1 3,882,462--"Fingerprint Recognition Apparatus Using Non-Coherent Optical Processing", issued May 6, 1975, PA1 3,891,968--"Coherent Optical Processor Apparatus With Improved Fourier Transform Plane Spatial Filter", issued June 24, 1975, and PA1 3,968,476--"Spurious Signal Removal in Optical Processor Identification Apparatus", issued July 6, 1976.
With respect to other well known prior art concepts which are generally antecedents of the foregoing, such as the standard computer processing technique which directly uses detailed images of fingerprints, these concepts attempt rather directly to imitate past manual or partially automated systems, such as those in which manually derived fingerprint measurements are entered into the memory of a data processor for electronic searching. However, the combination of prohibitive cost, low reliability, and low effective search speeds characterizes such approaches. The major problem exhibited by them is concerned with the large amount of data collected, so that to improve speed and accuracy, a decision must be made as to what information should actually be selected from that data total and how the selection can be most expeditiously accomplished to afford rapid, accurate operation.
An advantageous approach has been proven to be that used in principle in the above listed patents in which patterns of ridge angle data over the print surface are catalogued. For example, the merits of such ridge angle measurement and processing techniques are generally set forth in the D. H. McMahon, G. L. Johnson, S. L. Teeter, C. G. Whitney technical paper: "A Hybrid Optical Computer Processing Technique for Fingerprint Identification", I.E.E.E. Transactions on Computers, Vol. C-24, No. 4, April 1973, pages 358 through 369. It is found that the ridge angle representation of an original fingerprint pattern contains significantly less total data than a binary image representation of that original pattern and, in general, that the ridge angle representation adequately describes only the significant features of the original pattern, eliminating much unneeded data. Thus, approaches generating and using such ridge angle data are readily capable of more rapid operation in classifying fingerprint patterns and in fingerprint file searching based, for example, on the usual record file of ten prints. Inherent in the ridge angle data as a function of position on the print is the gross structure of the original pattern and the presence of cores and deltas, for example, is readily observed. Recognition of such features or descriptors not only supplies a means for extraction of significant data defining the structure of the print, but also guarantees that such descriptors will be independent of the positioning of the original print.
Even in the earliest classification systems, such as those based on four well-defined and highly reliable types; i.e., arches, left loops, right loops, and whorls, it is found that it is possible for significant numbers of people to have the same pattern types even on all ten respective fingers. Additional discrimination is customarily accomplished to a certain degree of success by counting the number of skin ridges between predetermined points on the fingerprint pattern. However, the additional discriminatory information thus derived is not fully sufficient, and reliable identification requires time-consuming visual examination of fine details of the prints, including special topological characteristics of the print pattern known as minutiae. The visual observation of the presence of minutiae such as bifurcations or ridge endings has been made, along with their spatial relationships in terms of ridge count and location relative to the aforementioned predetermined points. Before the use of computer minutiae comparison techniques, this final step in the determination of a true match was carried out only by visual inspection which, as noted, is expensive and time consuming.